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bennelson 02-01-12 02:26 PM

Compact Gasifier - wood-gas stove
Hey Guys,

I was over helping out at a friend's the other day. He has been working on a small gasifier stove.

The first two videos are ones he shot of the construction. The last video is what I shot the other day when some other people were over and we were test-firing it and measuring burn-time, fuel use, etc.

Essentially, the contraption burns wood chips with lots of heat, but little air to off-gas the voltatiles. Those then rise, where additional air is added to then burn that wood gas. It burns very clean on a small amount of fuel. Only charcoal is left over.

Daox 02-01-12 02:45 PM

Thanks for sharing Ben! Sounds like a cool project and one I'd be interested in (although I'm at work and can't see videos).

To embed the links you have to use the longer youtube URL.

bennelson 02-01-12 05:08 PM

OK, I fixed the links so you can just watch the videos embedded in the forum.

abogart 02-02-12 10:11 PM

He did a great job, very nice construction! What's really impressive is that it's actually useful. I made something very similar to that a few years back. It consisted of a coffee can and a soup can, but the design of the holes was almost exactly the same as this one. I didn't think of the chimney though, due to my limited knowledge of stove firing and natural draft back then. I must say that it's a very gratifying feeling when you first see those flames coming out of the top holes. That's when you shout to the wife "HONEY, C'MERE AND LOOK AT THIS!" ... and she just gives you this look like "and why are you burning sticks in a can out in the backyard???" And you say "but it's woodgas!" LOL!

It is an excellent little project to experiment with gasifiers though. The fact that he made it into a perfectly usable stove is all the more impressive. :thumbup:

Daox 02-03-12 08:36 AM

I assume a gasifier is more efficient than normal wood burning? Does anyone have any idea how much more efficient?

bennelson 02-03-12 09:21 AM

I can't give you scientific numbers on efficiency of a gasifier vs typical burning of wood, but.......

A gasifier makes use of more or less ALL the available chemical heat. Once it's going, the voltatile gasses all come out of the wood and are burned. On a typical wood fire (lets just imagine a camp fire or open fireplace) some of the volatile gasses burn, and some don't, they just float away. They are also a big part of what makes the smoke sting your eyes, and the smoke smell.

In the bottom of the gasifier, the left over "waste" is charcoal. That in itself can be used for all sorts of fun things. (Fuel, filtration, soil ammendment, etc.)

I really liked the size, shape, and look to this gasifier. I wan't to borrow it and take it camping.

ThomSjay 02-04-12 12:22 AM

This is very intriguing!
Can he try something else? Have the secondary rise higher above the fuel load before it enters the combustion chamber/chimney. I think this will "supercharge" the burn as was shown at the end of the last video with the fire roaring. Time had lapsed, the fuel level dropped as it was consumed which led to the secondary air being exposed longer and thus heated more. I got this idea from (abogart?) when he mentioned his work with the furnace at work where the temp increased rapidly.

abogart 02-04-12 08:47 AM

This is basically the same concept as the industrial heat recuperators that I worked with. One thing to watch out for with these small updraft gasifiers is the farther you place the secondary air ports away from the primary flame, the more chance there is for the secondary combustion to "flame out". It's not a big problem when it's running hot, but when adding fuel or when the fuel is running low, it might be more difficult to keep the secondary flame going. Remember that the secondary air absorbs heat from the hot primary gases. The longer the exchange between the two, the more cooling of the primary gases takes place. I think this is all part of "tuning" the design for optimal operation.

I had the idea that putting a displacer, like a closed pipe, inside the primary burn chamber starting just below the secondary air ports would force the gases around the outside of the chamber and promote more complete secondary combustion by reducing the amount of gas that can bypass the secondary air through the middle of the chimney.

Nonhog 06-03-13 10:30 AM

Can't watch above vids until I get home. Wonder if anyone has heard reviews on this.

My wife saw one at the Earth Fair yesterday and loved the idea.

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